1. Field of the Invention
The present invention relates to suppressing noise transmitted into a head of a hard disk drive.
2. Background Information
Hard disk drives contain a plurality of magnetic heads that are coupled to rotating disks. The heads write and read information by magnetizing and sensing the magnetic fields of the disk surfaces with separate write and read elements, respectively. Each head is attached to a flexure arm to create a subassembly commonly referred to as a head gimbal assembly (“HGA”). The HGA's are suspended from an actuator arm. The actuator arm has a voice coil motor that can move the heads across the surfaces of the disks.
The disks are rotated by a spindle motor of the drive. Rotation of the disks creates an air flow within the disk drive. Each head has an air bearing surface that cooperates with the air flow to create an air bearing between the head and the adjacent disk surface. The air bearing eliminates or minimizes the mechanical wear between the head and the disk. The height of the air bearing is commonly referred to as the flying height of the head.
The magnetic field detected by the head is inversely proportional to the flying height of the head. Likewise, the strength of the magnetic field written onto the disk is inversely proportional to the fly height. A larger fly height will produce a weaker magnetic field on the disk.
There have been developed heads that include a heater element. Current is provided to the heater element to generate heat and thermally expand the head to move the read and write elements closer to the disk. These types of heads are sometimes referred to as fly on demand (“FOD”) heads. The flying height of FOD heads can be varied by changing the amount of power provided to the heater element.
The heads are typically connected to a pre-amplifier circuit by a flexible cable that contains a number of internal conductive traces. For FOD heads there are typically 6 traces, two traces for the write element, two traces for the read element, a trace for the heater element and a ground trace.
Electrical noise, for example an electrostatic discharge, can be transmitted from the disk drive cover/base plate into the heads via the disk. This noise can travel through the head and into the ground and heater element traces of the flexible circuit. In typical flexible circuits, the ground and heater element traces are adjacent to the read traces. The noise on the ground and/or heater element traces can become coupled to the read traces. Noise in the read traces reduces the integrity of the read signal that is provided to the pre-amplifier circuit of the drive.